Psyshock is used for landing harder hits on specially-oriented walls in general aside from Chansey and Blissey. It also hits pre-Bulk Up Conkeldurr and Breloom hard without resorting to Draco Meteor. Also, when you see Chansey/Blissey, it's generally a better idea to Trick away your Choice item first, then switching to an appropriate counter.

Also, it's not a good idea to switch in Heatran on to Venusaur if Sleep Clause isn't active, but when it's active, Heatran can switch in to Venusaur safely.